1. Field of the Invention
The present invention is in the field of mold inhibitors and methods for making same, and it relates particularly to mold inhibitors for animal grain feeds.
2. Description of the Prior Art
There is a serious worldwide problem of molds growing in food materials, and particularly in animal feeds. This problem is most serious, and is a year-round problem, in tropical zones of both the eastern and western hemispheres, but it is also a problem in temperate and colder zones, particularly during the spring and fall seasons when there are frequently large temperature differentials between night and day, on the order of 30.degree. F. or more, which can cause an accumulation of moisture in the feed adjacent the cold metal of feed tanks or bins.
One reason why molds present such a serious problem is that they produce dangerous mycotoxins, some of which are
carcinogenic. For example, one of the common molds, Aspergillus flavus, produces the mycotoxin aflatoxin which, in addition to other toxic characteristics, interferes with the immune system's ability to produce gamma globulin, the protein that represents the immune system. The resulting breakdown of the immune system then renders animals that have ingested such mold vulnerable to a variety of diseases.
The standard product that has been used for many years for the control of molds is propionic acid ##STR1## CH.sub.3 CH.sub.3 COOH or C.sub.3 H.sub.7 O.sub.2 ]. Prior to the present invention, propionic acid has been the most reliable mold inhibitor for animal feeds, and it still remains the product of choice on a worldwide basis. However, propionic acid has serious problems, so that it is unacceptable in many circumstances, and its use will be limited in some areas of the world, particularly in the Orient where the mold problem is most severe. A major problem with propionic acid is that it has a terrible, strong odor, which is almost like the smell of urine, and when people work around propionic acid their clothes and bodies acquire this obnoxious odor. One reason for this bad odor is that it is very volatile, so that it is rapidly released in vapor form from feeds to which it has been applied. For this reason, many people, and the people of some regions such as the Orient, will not stand for the use of propionic acid; and those who do use it are uncomfortable in such use. Also, some animals, particularly hogs, and also goats, are especially sensitive to the odor of propionic acid and will not touch feed that contains any useful amount of propionic acid in it.
The other principal problem with propionic acid is that it is highly corrosive. The only feasible place for propionic acid to be applied to feeds is in the feed plants or mills, and these are made of mild steel which is particularly vulnerable to acid corrosion. Thus, feed mills in which propionic acid is added to the feeds will rapidly deteriorate from the attack of this acid.
A number of mold inhibitor products combining propionic acid with other ingredients such as acetic acid and benzoic acid have been and are currently being marketed under a variety of trademarks in an endeavor to make the products more commercially acceptable, but the principal operative ingredient of such products is still propionic acid, and such products still have the same problems of the odor and corrosiveness of propionic acid.
It has been understood in the art that it is the propionate ion or radical [CH.sub.3 CH.sub.3 COO, or C.sub.3 H.sub.6 O.sub.2 ] that is the active mold inhibitor ingredient in propionic acid, so attempts have been made to use salts of propionic acid as mold inhibitors in an endeavor to overcome the odor and corrosion problems. The principal salts that have been used are the sodium and calcium salts of propionic acid, and as far as the applicant is aware, these have only been used as mold inhibitors in a fine, granular form, and never in the form of a liquid solution. These propionate salts do not have an objectionable odor, and are neutral and hence not especially corrosive. The sodium propionate salt has been found satisfactory in solid form for human use in bread, this being made possible because the granular or powdered sodium propionate disperses fairly well in the wet bread dough, remaining well dispersed throughout the baked bread.
Although currently used to a limited extent in animal feeds, the dry propionate salts are not satisfactory for feeds, the principal problem being that in granular form there is insufficient contact of the propionate salt particles with the grain particles unless great quantities of the propionate salts are used. On the order of five to seven times as much of the propionate salt must be used in order to disperse it adequately through the feed to get approximately the same degree of mold inhibition as can be achieved with liquid propionic acid. This makes the use of dry propionic salts such as sodium propionate and calcium propionate economically disadvantageous as mold inhibitors for animal feeds.
Prior to the present invention, propionic acid salts have never been usable in the form of a liquid solution for treating animal feeds, even though they would be equally as effective as mold inhibitors as propionic acid because it is the propionate ion which performs the mold inhibiting function, and the liquid would be readily dispersable in intimate contact with the feed grain particles in the same relatively small amounts as with liquid propionic acid, but without the objectionable odor and corrosive characteristics of the acid. It is believed that the principal reason why liquid propionic salt solutions have not heretofore been used as animal feed, mold inhibitors is the great propensity of the propionic salts to precipitate out of the solution in a mushy, gel-like form. This precipitation tendency is so great that a stable propionate salt solution of sufficient concentration to be a useful product has heretofore never been achieved. Even though adequate concentrations might have been achievable under controlled laboratory or plant conditions, the long-term stability was entirely inadequate for a useful mold inhibiting product.
There is also a serious mold problem which occurs in feeds that are stored in metal feed tanks or bins at locations where there are large overnight temperature drops, on the order of 30.degree.-40.degree. F., even with feeds that have a low moisture content. Such large temperature drops will lower the temperature of the feed bin or tank itself, establishing a large temperature differential between the walls of the tank or bin and the temperature of the feed within the central region of the tank. Water molecules have the characteristic of moving from a warmer zone toward a colder zone, and thus will move from the central region of the tank through the feed itself toward the cold walls of the tank, increasing the humidity and dampening the feed near the walls to provide an excellent growing medium for molds in that region; and this is recognized as a major problem when the humidity level increases to the point where moisture actually condenses on the walls of the tank. After a few repeated nights of a temperature differential on the order of 30.degree.-40.degree. F., mold spores which are present all of the time will become active and propagate. Even with feed having an average moisture content of 13.5 percent or less, which is normally considered to be safe from any substantial mold problem, the moisture content in the feed adjacent the tank walls will be raised higher and higher night after night of such temperature differentials, and a substantial mold problem will develop.